Tuesday, 3 September 2013

ZBA Guard's Van Construction Tips

ZBA Main Body Section
The ZBA brake van is printed in two sections.  The main section consists of one side, the roof, ends, and floor.  The other section consists of the other side, including the running boards for that side.

ZBA Flat Side Section

Removing Support Structures

Carefully remove the support structure from both parts of the guard's van.  It is suggested to use a sharp knife  carefully cut the supports away from the roof, ends, and the underframe.  Take particular care around the running boards, brake hoses, the brake gear underneath the floor, and the dividing bars between the double windows.

Be very careful removing the support structures from the open side of the main body section.  Close to the centre, there is a projecting brake shaft, pictured below.  To avoid damaging the brake shaft, it is suggested to remove the supports from around it first.

Brake Shaft
There will be a support on the very end of the brake shaft.  Try to leave approximately 0.5 mm of the narrowed section where the supports is attached to the brake shaft, as this forms a pin which interlocks with a hole in the side section to support the free end of the brake shaft.
Brake Shaft Pin Detail
Because of the ribbing on the brake hoses, the 3D printer's automatic software has generated many support points, which may have merged into one.  Carefully cut between the brake hose and the support structure, using repeated cuts with a sharp knife (e.g. Olfa snap-off blade type), to separate the support structure, then carefully trim the remnants from the hose.

Once the majority of the support structure has been removed, carefully go over both parts and cut away the small supports which typically extend from one part to another, for example, around the brake rigging.  An Exacto type hobby knife with a sharp pointed blade (Exacto #11 or similar) is quite useful for getting into the nooks and crannies.

Go over the model and smooth off any remnants of the fine supports, especially on the edge of the roof on the open side of the main body section.  A sanding stick or small file can be useful for this

When finished, test fit the two halves together.  Interlock the tabs on the top of the flat side under the roof of the main section, then gently move the flat side into position to see how it fits.   There are three tabs on the bottom of the flat side which should end up on top of the floor surface, inside the main part of the van.

Tapping Holes

The mounting holes for the couplers and bogies should be tapped 2-56 (or 8BA).  As printed, the holes are 1.8 mm dia.  Clear out the holes with a 1.8 mm drill in a pin vice, and drill through the floor as well to faciliate tapping.

If desired, the holes in the three tabs on the inside of the flat wall section can be tapped to all the side wall to be fixed in place with screws, rather than glue, to allow for future access to the inside.

Note:  Tapping the holes is preferable to using self-tapping screws which may fracture the material.  Although fairly robust, the material is more brittle than styrene or polyurethane.  


The spigots on the underframe are designed to suit Walthers bogies Part No. 933-1077.  Other types of bogies can be fitted by cutting away the spigots as required, and building up a mounting platform at the required height from styrene sheet.  If using different bogies, ensure that the mounting height is adjusted so that the coupler mounting surface is 11.5 mm above rail level.

If using the Walthers bogies, the bogies should be dismantled to allow fitting of 12 mm diameter spoked wheels (26 mm axle length).  With care, the brake shoes at the ends of the bogie sideframes can be bent out to provide clearance for the 12 mm wheels.  The bogies are supplied with spare bolsters which have a high mounting boss, and these spare bolsters should be used when reassembling the bogies.

When fitted with the Walthers bogies, the ZBA will negotiate curves down to 600 mm radius.


The ZBA is designed for Kadee "whisker" couplers.  Either the #158 (scale size) or #148 (normal size) couplers can be used, with #262 draft gear boxes.

The draft gear boxes supplied with the couplers do not fit as they have a different mounting hole position.  The #262 draft gear boxes are narrower and have been used because they allow details such as the brake hoses to be positioned the scale distance from the van centre line.  Also, the #262 draft gear boxes are easier to use as the lid snaps into position.

Note that the height from rail level to the coupler mounting surface should be 11.5 mm, the standard for Kadee couplers.

Truss Rods

The truss rods can be formed from 0.5 or 0.6 mm brass wire. From a length 94.5 mm long, form a 10° bend 30 mm in from each end, to leave a horizontal section 34.5 mm long.

There are grooves in the lower running boards and running board support brackets into which the truss rods can be glued.  Between the queen posts, the truss rods run on the underside of the lower running boards.  The small projections below the side sills represent the brackets which anchor the truss rod ends on the real guard's van, so the ends of the truss rods should finish in line with these brackets.

Optionally, the truss rods could be extended horizontally at each (e.g. by 5 mm) and glued onto the underside of the side sills for additional strength.

Truss Rod Location (rear view of Flat Side)


Small starter holes have been provided to locate the various handrails.

The long handrails on each side can be cut from ?? mm brass wire.  Turned brass handrail knobs are available in various lengths, to allow for the thickness of the doors (1.5 mm), so that the handrails remain parallel to the sides.

The small handrails can be formed from 0.5 mm brass wire.  These include the diagonal handrails on each door, and the horizontal handrail on each door below the long handrail.


With the recommended bogies, the completed van weighs around 82 grams.  The "desirable" weight for a van of that length (140 mm) is around 95 grams to ensure optimum operation including operation of Kadee couplers.  (See the Sn3½ blog for more information.)

Additional weight can be added by gluing lead shot or sheet lead between the various frame members of the underframe, where it would not be seen in normal operation, or gluing sheet lead on the floor inside the van.


Either enamel or acrylic hobby paints can be used to paint the finished model.